CN116111444B - Laser and preparation method thereof - Google Patents
Laser and preparation method thereof Download PDFInfo
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- CN116111444B CN116111444B CN202211089099.8A CN202211089099A CN116111444B CN 116111444 B CN116111444 B CN 116111444B CN 202211089099 A CN202211089099 A CN 202211089099A CN 116111444 B CN116111444 B CN 116111444B
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 50
- 229910052581 Si3N4 Inorganic materials 0.000 claims description 41
- 229910021420 polycrystalline silicon Inorganic materials 0.000 claims description 41
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 claims description 41
- 239000000463 material Substances 0.000 claims description 40
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
- H01S5/026—Monolithically integrated components, e.g. waveguides, monitoring photo-detectors, drivers
- H01S5/0268—Integrated waveguide grating router, e.g. emission of a multi-wavelength laser array is combined by a "dragon router"
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/12—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers
- H01S5/1231—Grating growth or overgrowth details
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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- General Physics & Mathematics (AREA)
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- Optics & Photonics (AREA)
- Semiconductor Lasers (AREA)
Abstract
The embodiment of the application discloses a laser and a preparation method of the laser, wherein the laser comprises a substrate, a grating waveguide structure sharing the substrate, a passive waveguide structure and a DFB laser structure, in the use process, the laser is excited by applying forward voltage to generate laser, part of the laser enters the passive waveguide structure from the grating waveguide structure, the two ends of an FP cavity of the passive waveguide structure are high in reflectivity, the FP cavity can promote the cavity length, and negative feedback can be provided for the DFB structure to stabilize the wavelength of the laser, so that the line width is compressed. The light has little loss in the passive waveguide structure. The laser provided by the embodiment of the application truly realizes the efficient coupling of the laser and the FP feedback cavity, and can provide high reflectivity for one end surface of the FP cavity, which cannot be coated with the film, so that the feedback effect of the FP cavity is improved.
Description
Technical Field
The embodiment of the application relates to the technical field of semiconductor devices, in particular to a laser and a preparation method of the laser.
Background
In the field of optical communication, a narrow linewidth semiconductor laser plays an important role in coherent optical communication and a wavelength division multiplexing system, and the application requirement of long-distance transmission requires that the laser works in a C band with the lowest optical fiber transmission loss, so that the communication system can realize lower transmission delay, phase jitter and bit error rate. One of the main reasons for limiting the error rate and phase jitter performance of the system is the linewidth, noise and polarization stability of the signal light.
In the field of vehicle-mounted laser radars, traditional high-precision radar technologies such as microwave radars, millimeter wave radars and the like are not suitable for intelligent automobile carrying due to low detection precision, large size and heavy weight, but are used as ideal light sources of all-solid-state laser radars, and the narrow-linewidth semiconductor laser has the advantages of high resolution, strong active interference resistance, small size, light weight, low cost and the like, so that the requirements of future intelligent automobiles on the high-precision detection technology can be met. In addition, narrow linewidth lasers have many applications in the fields of optical sensing, optical measurement, satellite communications, and the like.
According to Langiwan noise theory, it can deduce the modified Shore-Tang Si equation for semiconductor laser, the intrinsic linewidth of which is positively correlated with the spontaneous emissivity of the laser, the optical confinement factor and the linewidth broadening factor, and the photon density in the resonant cavity and the photon life are negatively correlated. Therefore, when designing a narrow linewidth semiconductor laser, firstly, reducing the linewidth broadening factor of the semiconductor laser and suppressing the spontaneous emission of the laser are considered, which requires to increase the differential gain coefficient of the material; furthermore, increasing photon density requires increasing the optical power output of the laser, which means that the active part of the semiconductor laser needs to have very high gain and low loss absorption. The two aspects need to design a chip structure with high differential gain and saturation gain; since the laser photon lifetime is proportional to the cavity length, narrow linewidth lasers require very long cavities.
Based on the above principle, the conventional technology mainly adopts the following two ways to design a narrow linewidth semiconductor laser:
intracavity optical feedback (integrating frequency selective structures in the resonator): the design is mainly based on a DFB laser and a DBR laser, but the narrow linewidth lasers need to carry out complex design on a grating and an epitaxial structure, and the manufacturing process is complex and needs multiple epitaxy and high-precision equipment; in addition, the doped waveguide structure has strong light field absorption particularly in the P-type doped region and the multiple quantum well structure, if the cavity length is simply increased, the loss is greatly increased, the output power of the laser is reduced, the threshold current is increased, and the defect limits the line width of the semiconductor laser in the cavity.
External cavity optical feedback method (coupling device with mode selection function outside optical cavity): the external cavity optical feedback method narrow linewidth semiconductor laser is characterized in that an optical element such as a fiber bragg grating waveguide structure is arranged outside an optical cavity, and the optical emitted by a gain chip is subjected to frequency selection and feedback by a Fabry-Perot filter and the like, so that the linewidth is compressed. The laser has the advantages that no internal grating is lost, the performance of the laser is excellent, the theoretical linewidth is very narrow, but the requirement on the external working environment is high, and various humiture, vibration and the like can influence the performance of the laser; the requirements on the coupling light paths of the optical elements are high, the optical elements are required to be precisely aligned, and the requirements on the packaging process are high.
Disclosure of Invention
The present invention aims to solve at least one of the technical problems existing in the prior art or related art.
To this end, a first aspect of the invention provides a laser.
The second aspect of the invention provides a method of manufacturing a laser.
In view of this, a first aspect according to an embodiment of the present application proposes a laser comprising:
a substrate;
a grating waveguide structure disposed on the substrate;
the passive waveguide structure is arranged on the substrate and is positioned at one side of the grating waveguide structure;
and the DFB structure is arranged on the substrate and positioned on the other side of the grating waveguide structure.
In one possible embodiment, the grating waveguide structure comprises:
the first silicon oxide cladding layer, the polysilicon grating layer, the silicon nitride grating cover layer and the second silicon oxide cladding layer are sequentially arranged upwards to the substrate;
the refractive index of the polysilicon grating layer is larger than that of the first silicon oxide cladding layer and the second silicon oxide cladding layer, the refractive index of the silicon nitride grating covering layer is larger than that of the first silicon oxide cladding layer and the second silicon oxide cladding layer, and the refractive index of the silicon nitride grating covering layer is smaller than that of the polysilicon grating layer.
In a possible implementation manner, the polysilicon grating layer is formed with a plurality of first convex parts, and the silicon nitride grating cover layer is formed with a plurality of second convex parts, and the second convex parts are positioned between two adjacent first convex parts;
wherein, the first convex part is the same with the height of second convex part, and the width is different, and the width of first convex part and second convex part satisfies following formula:
d＝(2m+1)λ/4n
wherein d is the width of the first convex part and the second convex part, n is the refractive index of each layer of material, m is a positive integer lambda is the lasing wavelength of the laser.
In one possible embodiment, the passive waveguide structure includes:
the lower cladding layer, the waveguide layer and the upper cladding layer are sequentially arranged upwards from the substrate;
wherein the lower cladding layer, the waveguide layer and the upper cladding layer are undoped.
In one possible embodiment, the DFB structure includes:
the buffer layer, the lower limiting layer, the multiple quantum well layer, the upper limiting layer, the electron blocking layer, the spacing layer, the corrosion stopping layer, the spacing layer, the grating cover layer, the protective layer and the ohmic contact layer are sequentially arranged upwards to the substrate;
wherein the thickness of the first limiting layer is 200nm to 500nm, the thickness of the second limiting layer is 80nm to 120nm, and the thickness of the electron blocking layer is 20nm to 50nm.
In one possible embodiment, the laser further comprises:
a first electrode layer overlying the DFB structure;
a second electrode layer covering a side of the substrate facing away from the grating waveguide structure, the passive waveguide structure, and the DFB structure;
wherein the substrate is an InP substrate.
According to a second aspect of embodiments of the present application, a method for preparing a laser according to any one of the above technical solutions is provided, where the method includes:
preparing a grating waveguide structure on a substrate;
preparing a passive waveguide structure on the substrate and positioned at one side of the grating waveguide structure;
and preparing a DFB structure on the substrate and positioned on the other side of the grating waveguide structure.
In a possible embodiment, the step of preparing a grating waveguide structure on a substrate comprises:
growing a first silicon oxide film and a polysilicon film on the substrate;
etching the polysilicon film to form a polysilicon grating layer;
depositing silicon nitride on the polysilicon grating layer to form a silicon nitride layer;
depositing a second silicon dioxide film on the silicon nitride grating cover layer;
and etching the first silicon oxide film, the polycrystalline silicon grating layer, the silicon nitride layer and the second silicon oxide film to form the grating waveguide structure on the substrate.
In a possible embodiment, the step of preparing a passive waveguide structure on the substrate and at one side of the grating waveguide structure includes:
shielding the grating waveguide structure and a portion of the substrate;
a lower cladding layer, a waveguide layer and an upper cladding layer are sequentially grown on the substrate and positioned on one side of the grating waveguide structure;
wherein, the preparation materials of the lower cladding layer and the upper cladding layer comprise InP materials, and the preparation materials of the waveguide layer comprise InGaAsP and/or AlGaInAs materials;
wherein the bandgap of the material used to make the waveguide layer is greater than the bandgap of the material used to make the multiple quantum well layer of the DFB structure.
In a possible embodiment, the step of preparing a DFB structure on the substrate and on the other side of the grating waveguide structure includes:
shielding the grating waveguide structure and the passive waveguide structure;
growing an InP doped buffer layer on the substrate and on the other side of the grating waveguide structure;
growing an N-type light limiting layer on the buffer layer to form a first limiting layer;
growing a multiple quantum well layer on the first confinement layer;
growing an intrinsic second confinement layer on the multiple quantum well layer;
growing a P-type electron blocking layer on the second limiting layer;
growing a first InP spacer layer on the P-type electron blocking layer, forming an etching stop layer on the InP spacer layer, and then growing a second InP spacer layer on the etching stop layer;
preparing a grating on the second InP spacer layer;
growing a grating covering layer with gradually increased doping concentration on the grating;
sequentially preparing a cladding layer and an ohmic contact layer on the grating covering layer;
the preparation method further comprises the following steps:
a first electrode is formed on the DFB structure and a second electrode is formed on a side of the substrate facing away from the grating waveguide structure, the passive waveguide structure, and the DFB structure.
Compared with the prior art, the invention at least comprises the following beneficial effects: the laser provided by the embodiment of the application comprises the substrate, the grating waveguide structure sharing the substrate, the passive waveguide structure and the DFB structure, and in the use process, the laser is excited by applying forward voltage to generate laser, part of the laser enters the passive waveguide structure from the grating waveguide structure, the two ends of the FP cavity of the passive waveguide structure are high in reflectivity, the cavity length of the FP cavity can be increased, the wavelength of the laser can be stabilized for the DFB structure through negative feedback, and the line width is further compressed. The light has little loss in the passive waveguide structure. Through the arrangement of the grating waveguide structure, on one hand, the light of the laser can be efficiently coupled into the passive waveguide structure, meanwhile, high reflectivity can be provided for one end face of the passive waveguide structure, which cannot be coated by the FP cavity, so that the reflectivity of the FP cavity can be higher than 70%, the effect of compressing the line width can be well achieved, based on the laser provided by the embodiment of the application, the advantages of an external cavity optical feedback method and an internal cavity optical feedback method can be combined, the high-power DFB laser, the FP feedback cavity and the grating waveguide structure are monolithically integrated to form the high-performance narrow-line-width laser, the laser has the advantages of the external cavity optical feedback method and the internal cavity optical feedback method, the monolithic integration does not need a plurality of optical elements for coupling, the feedback cavity and the laser can be independently designed, and the cavity length of the resonant cavity is not limited by the internal loss of the DFB laser. In addition, the high-efficiency coupling of the laser and the FP feedback cavity is truly realized by arranging the grating waveguide structure, and the high-reflectivity optical fiber can provide high reflectivity for one end surface of the FP cavity, which cannot be coated with a film, so that the feedback effect of the FP cavity is improved.
Drawings
Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the application. Also, like reference numerals are used to designate like parts throughout the figures. In the drawings:
FIG. 1 is a schematic block diagram of a laser according to one embodiment provided herein;
FIG. 2 is a schematic step flow diagram of a method of fabricating a laser according to one embodiment provided herein;
FIG. 3 is a schematic diagram of a first state of a fabrication method of a laser to fabricate a grating waveguide structure according to one embodiment provided herein;
FIG. 4 is a schematic diagram of a second state of a fabrication method of a laser to fabricate a grating waveguide structure according to one embodiment provided herein;
FIG. 5 is a schematic diagram of a third state of a fabrication method of a laser to fabricate a grating waveguide structure according to one embodiment provided herein;
FIG. 6 is a schematic diagram of a fourth state of a method of fabricating a grating waveguide structure according to one embodiment of the laser provided herein;
FIG. 7 is a schematic diagram of a fifth state of a method of fabricating a grating waveguide structure according to one embodiment of the laser provided herein;
FIG. 8 is a schematic diagram of a method of fabricating a passive waveguide structure for a laser according to one embodiment provided herein;
fig. 9 is a schematic diagram of a DFB structure prepared by a method of preparing a laser according to one embodiment provided herein;
fig. 10 is a step diagram of a chip process flow of a method for manufacturing a laser according to an embodiment of the present application
Fig. 11 is a schematic diagram of a multilayer film reflectivity curve of a laser according to one embodiment provided herein.
Wherein, the correspondence between the reference numerals and the component names in fig. 1 and fig. 2 to fig. 9 is:
a 110 substrate, a 120 grating waveguide structure, a 130 passive waveguide structure, a 140DFB structure, a 150 first electrode layer, a 160 second electrode layer;
121 a first silicon oxide cladding layer, 122 a polysilicon grating layer, 123 a silicon nitride grating cover layer, 124 a second silicon oxide cladding layer;
131 lower cladding, 132 waveguide layer, 133 upper cladding;
141 buffer layer, 142 first confinement layer, 143 multiple quantum well layer, 144 second confinement layer, 145 electron blocking layer, 146 grating, 147 cladding layer, 148 ohmic contact layer, and etch stop layer 149.
Detailed Description
In order to better understand the technical solutions described above, the technical solutions of the embodiments of the present application are described in detail below through the accompanying drawings and the specific embodiments, and it should be understood that the embodiments of the present application and the specific features in the embodiments are detailed descriptions of the technical solutions of the embodiments of the present application, and not limit the technical solutions of the present application, and the embodiments of the present application and the technical features in the embodiments of the present application may be combined with each other without conflict.
As shown in fig. 1, 2 to 9, according to a first aspect of an embodiment of the present application, a laser is provided, including: a substrate 110; a grating waveguide structure 120 disposed on the substrate 110; a passive waveguide structure 130 disposed on the substrate 110 on one side of the grating waveguide structure 120; the DFB structure 140 is disposed on the substrate 110 on the other side of the grating waveguide structure 120.
The laser provided by the embodiment of the application includes the substrate 110, and the grating waveguide structure 120, the passive waveguide structure 130 and the DFB structure 140 sharing one substrate 110, in the use process, the laser is excited by applying a forward voltage to generate laser, a part of the laser enters the passive waveguide structure 130 from the grating waveguide structure 120, the two ends of the FP cavity of the passive waveguide structure 130 are both high in reflectivity, the FP cavity can not only raise the cavity length, but also can provide negative feedback for the DFB structure 140 to stabilize the wavelength of the laser, and further the linewidth is compressed.
The light has little loss in the passive waveguide structure 130. By the arrangement of the grating waveguide structure 120, on one hand, the light of the laser can be efficiently coupled into the passive waveguide structure 130, and meanwhile, high reflectivity can be provided for one end surface of the passive waveguide structure 130, which cannot be coated with a film, so that the reflectivity of the FP cavity can be over 70%, and the effect of compressing the line width can be well achieved.
The laser provided by the embodiment of the application can combine the advantages of the external cavity optical feedback method and the internal cavity optical feedback method, the high-power DFB laser, the FP feedback cavity and the grating waveguide structure 120 are monolithically integrated to form a high-performance narrow linewidth laser, the laser has the advantages of the external cavity optical feedback method and the internal cavity optical feedback method, the monolithic integration does not need a plurality of optical elements for coupling, the feedback cavity and the laser can be independently designed, and the cavity length of the resonant cavity is not limited by the internal loss of the DFB laser. In addition, by arranging the grating waveguide structure 120, the efficient coupling of the laser and the FP feedback cavity is truly realized, and the high reflectivity can be provided for one end surface of the FP cavity, which cannot be coated, so that the feedback effect of the FP cavity is improved.
As shown in fig. 1, 2-9, in one possible embodiment, the grating waveguide structure 120 includes: a first silicon oxide cladding layer 121, a polysilicon grating layer 122, a silicon nitride grating cover layer 123, and a second silicon oxide cladding layer 124 disposed in this order up to the substrate 110; wherein, the refractive index of the polysilicon grating layer 122 is greater than the first silicon oxide cladding layer 121 and the second silicon oxide cladding layer 124, the refractive index of the silicon nitride grating cover layer 123 is greater than the first silicon oxide cladding layer 121 and the second silicon oxide cladding layer 124, and the refractive index of the silicon nitride grating cover layer 123 is less than the refractive index of the polysilicon grating layer 122.
In this technical solution, there is further provided a structural composition of the grating waveguide structure 120, where the grating waveguide structure 120 includes a 4-layer structure, a first silicon oxide cladding 121 with a low refractive index, a polysilicon grating layer 122 with a high refractive index, a silicon nitride grating cover layer 123 with a high refractive index, and a second silicon oxide cladding 124 with a low refractive index in order from bottom to top; the refractive index of the first silica cladding 121 and the second silica cladding 124 may be 1.44, the refractive index of the polysilicon grating layer 122 is 3.48, and the refractive index of the silicon nitride grating cover layer 123 is 2.0, so that a slab waveguide structure is formed, so that the grating waveguide structure 120 can efficiently couple the light of the laser into the passive waveguide structure 130 on one hand, and simultaneously, can provide a high reflectivity for one end surface of the passive waveguide structure 130, which cannot be coated with a film, so that the reflectivity of the FP cavity can well play a role of compressing the line width at more than 70%.
It will be appreciated that the grating waveguide structure 120 functions in that, on the one hand, it is realized that the waveguide structure couples light of the DFB laser into the FP cavity; on the other hand, the effect of controlling the refractive index of the FP cavity is achieved.
The principle of the grating waveguide structure 120 is that when light is incident from a high refractive index material to a low refractive index material, the light intensity of the refracted light is zero when the incident angle exceeds a certain angle, namely, the total reflection phenomenon, the light tends to propagate in the high refractive index material from the appearance, for the invention, the refractive index of the grating structure formed by polysilicon and silicon nitride is larger than that of the silicon oxide cladding layer, so the light propagates into the waveguide structure of the FP cavity in the grating, and therefore, the propagation loss of the light emitted by the DFB laser in the waveguide is small; if the light without the structure DFB laser has a divergence angle (similar to the light of a flashlight) due to diffraction effect to propagate a distance to the FP cavity, only a small part of the light can be coupled into (enter) the FP cavity for feedback;
in a possible implementation manner, a grating structure is formed on the polysilicon grating layer 122 by etching, then a silicon nitride grating cover layer 123 is deposited, a plurality of periodic silicon oxide and silicon nitride alternately arranged grating structures are formed, a plurality of first convex parts are formed on the polysilicon grating layer 122, a plurality of second convex parts are formed on the silicon nitride grating cover layer 123, the second convex parts are positioned between two adjacent first convex parts, and the plurality of convex parts form the grating structure; wherein, the first convex part is the same with the height of second convex part, and the width is different, and the width of first convex part and second convex part satisfies following formula:
d＝(2m+1)λ/4n
wherein d is the width of the first convex part and the second convex part, n is the refractive index of each layer of material, m is the positive integer lambda is the lasing wavelength of the laser, and the value is 1550nm or 1310nm.
In this technical solution, a pattern of contact sides of the polysilicon grating layer 122 and the silicon nitride grating cover layer 123 is further provided, the contact sides of the polysilicon grating layer 122 and the silicon nitride grating cover layer 123 form first protrusions and second protrusions which are alternately arranged, and refractive indexes of the polysilicon grating layer 122 and the silicon nitride grating cover layer 123 are different, so that a multi-layer film structure with alternately arranged high and low refractive indexes is formed on the contact sides of the polysilicon grating layer 122 and the silicon nitride grating cover layer 123, according to the reflectivity of the multi-layer film, the film thickness of each layer film can be calculated by (2m+1) λ/4n (m is a positive integer), the heights of the first protrusions and the second protrusions can be determined according to the laser wavelength of DFB, and the arrangement circumference of the first protrusions and the second protrusions can determine the reflectivity, based on this, by controlling the arrangement Zhou Qin of the grating 146 through an etching process, the waveguide length of the grating 146 can be controlled to be 70% to 95%, so that the waveguide structure 120 can efficiently couple the light of the laser into the passive waveguide structure 130, and simultaneously, according to the reflectivity of the passive waveguide 130 can not be well compressed by the passive waveguide structure, and the passive waveguide 130 can not be provided with a high reflectivity of the passive cavity width 70%.
The grating waveguide structure combined with the application is a structure in which high-refractive-index polysilicon and low-refractive-index silicon nitride are alternately arranged, and the widths of the first convex part and the second convex part are also defined by a formula. This structure provides high reflectivity to the FP cavity, with the wavelength on the middle horizontal axis and reflectivity on the vertical axis in fig. 11. Taking 1550nm as an example, the reflectivity of one period with high and low reflectivity is 68%, the reflectivity of 2 periods with high and low reflectivity can reach 87%, and the requirement can be met by the grating with two periods. It should be noted that, in the actual process, the refractive index and the film thickness of the film layer may fluctuate within a certain range, which eventually results in that the reflectivity may also fluctuate around the theoretical value. Therefore, by controlling the number of periods of the grating, we can control the reflectivity of the FP cavity.
The linewidth of a compressed laser providing feedback through the FP cavity requires a reflectivity of 70%, preferably over 80%, and only at this reflectivity the feedback of the FP cavity to the laser can be standardized.
As shown in fig. 1, 2-9, in one possible embodiment, the passive waveguide structure 130 includes: a lower cladding layer 131, a waveguide layer 132, and an upper cladding layer 133 disposed in this order up to the substrate 110; wherein the lower cladding layer 131, the waveguide layer 132 and the upper cladding layer 133 are undoped.
In this technical solution, there is further provided a structure composition of the passive waveguide structure 130, where the passive waveguide structure 130 may include a lower cladding layer 131, a waveguide layer 132, and an upper cladding layer 133 sequentially disposed, and the lower cladding layer 131, the waveguide layer 132, and the upper cladding layer 133 are not doped, so that during the operation of the laser, since the passive waveguide structure 130 is undoped, the bandgap of the passive waveguide structure 130 is higher than the bandgap of the multiple quantum well of the DFB structure 140, and thus light is hardly lost in the passive waveguide segment.
The three-layer structure of the lower cladding layer 131, the waveguide layer 132, and the upper cladding layer 133 can make light propagate only in the waveguide layer, and reduce loss when light propagates.
The passive waveguide structure 130 operates on the principle that: the refractive index of the waveguide layer 132 is higher than that of the upper and lower cladding layers 131, and the 3 layers form a slab waveguide structure, so that most of light can propagate in the waveguide layer 132 with high refractive index; the band gap of the material of the waveguide layer 132 is higher than that of the multiple quantum well of the DFB laser, and the material itself cannot absorb light emitted by the DFB laser; the 3 layers of films are undoped, so that light absorption caused by doping does not exist; in summary, the passive waveguide structure 130 forms an FP cavity with very little optical loss.
As shown in fig. 1, 2-9, in one possible embodiment, DFB structure 140 includes: a buffer layer 141, a first confinement layer 142, a multiple quantum well layer 143, a second confinement layer 144, an electron blocking layer 145, a first spacer layer, an etch stop layer 149, a second spacer layer, a grating 146, a grating cover layer, a protective layer 147, and an ohmic contact layer 148 disposed in this order up to the substrate 110; wherein the thickness of the first confinement layer 142 is 200nm to 500nm, the thickness of the second confinement layer 144 is 80nm to 120nm, and the thickness of the electron blocking layer 145 is 20nm to 50nm.
In this embodiment, the DFB structure 140 further includes, in order from the substrate 110, a Buffer layer 141, a first confinement layer 142, a multiple quantum well layer 143, an upper confinement layer 144, an electron blocking layer 145, a spacer layer, an etch stop layer 149, a spacer layer, a grating 146, a grating cladding layer, a cladding layer 147 (InP cladding), and an ohmic contact layer 148. Wherein the thickness of the first confinement layer 142 is 200nm to 500nm, and the graded doping is (1.fwdarw.0.7). Times.10 18 cm -3 The method comprises the steps of carrying out a first treatment on the surface of the The thickness of the second limiting layer 144 is 80nm to 120nm, and the second limiting layer is undoped; the thickness of the electron blocking layer 145 is 20-50nm, and the light P type doping is 0.7X10 18 cm -3 The method comprises the steps of carrying out a first treatment on the surface of the The laser cavity length is 600um to 1200um.
The buffer layer 141 may reduce defects due to the substrate; the first confinement layer 142 and the second confinement layer 144 are waveguide layers, mainly providing optical field confinement, and the lower confinement layer is wider than the upper confinement layer to confine the optical field to the N-plane and reduce absorption of P-plane light; the multiple quantum well layer 143 may provide a gain medium light emitting region; grating 146 grating cover: providing mode-selective action to enable the laser to operate in a single longitudinal mode with a κl of 0.4 to 0.8; etch stop layer 149: the corrosion cannot be continued when the corrosive liquid corrodes the layer, so that over-corrosion can be prevented; the electron blocking layer 145 may prevent electrons from leaking to the P region; cladding 147 may be subsequently made into a ridge waveguide; the ohmic contact layer 148 may provide an ohmic contact to reduce the laser resistance.
In one possible embodiment, the laser further comprises: a first electrode layer 150 overlying the DFB structure 140; a second electrode layer 160 covering a side of the substrate 110 facing away from the grating waveguide structure 120, the passive waveguide structure 130, and the DFB structure 140; wherein the substrate 110 is an InP substrate 110.
The first electrode 150 is a positive electrode, and the second electrode 160 is a negative electrode, which plays a role in energizing the DFB laser; in addition, the laser has the function of radiating heat.
In some examples, the first electrode layer 150 and the second electrode are Ti/Pt/Au electrodes, the DFB structure 140 of the laser is plated with a high transmittance thin film (AR film), the emissivity of the AR film is <1%; the end face of the passive waveguide structure 130 of the laser is HR film coated with a reflectivity >90%.
In some examples, the waveguides of the grating waveguide structure 120, the passive waveguide structure 130, and the DFB structure 140 are aligned, the buffer layer 141 has a thickness of 500nm, the total thickness of the upper and lower waveguides plus the multiple quantum well is 300nm to 650nm, the thicknesses of the grating waveguide structure 120 and the lower cladding layer 131 of the passive waveguide structure 130 are also 500nm, and the thicknesses of the waveguide layer 132 are also 300nm to 650nm. The arrangement can realize the high-efficiency coupling of light in 3 structures, and the working principle is as follows: principle of: the above-described technical effects are described based on the fact that the thickness of each layer of the DFB laser is defined as above, and the principle of light propagation in the slab waveguide is also described. The refractive index of the first confinement layer 142 and the second confinement layer 144 and the multiple quantum well layer 143 in the DFB laser is higher than that of the other layers, so that the layers are waveguide layers of the slab waveguide, and light propagates in the layers. In order to achieve efficient coupling of light in 3 structures. It will be appreciated that the position and thickness of the waveguides of the 3 structures must be guaranteed to be the same.
As shown in fig. 1 to 10, a method for manufacturing a laser according to a second aspect of an embodiment of the present application is provided, where the method for manufacturing a laser according to any one of the foregoing technical solutions includes:
step 101: preparing a grating waveguide structure on a substrate;
step 102: preparing a passive waveguide structure on the substrate and positioned at one side of the grating waveguide structure;
step 103: a DFB structure is fabricated on the substrate and on the other side of the grating waveguide structure.
The traditional technology mainly adopts the following two ways to design a narrow linewidth semiconductor laser:
intracavity optical feedback (integrating frequency selective structures in the resonator): the design is mainly based on a DFB laser and a DBR laser, but the narrow linewidth lasers need to carry out complex design on a grating and an epitaxial structure, and the manufacturing process is complex and needs multiple epitaxy and high-precision equipment; in addition, the doped waveguide structure has strong light field absorption particularly in the P-type doped region and the multiple quantum well structure, if the cavity length is simply increased, the loss is greatly increased, the output power of the laser is reduced, the threshold current is increased, and the defect limits the line width of the semiconductor laser in the cavity.
External cavity optical feedback method (coupling device with mode selection function outside optical cavity): the external cavity optical feedback method narrow linewidth semiconductor laser is characterized in that an optical element such as a fiber bragg grating waveguide structure is arranged outside an optical cavity, and the optical emitted by a gain chip is subjected to frequency selection and feedback by a Fabry-Perot filter and the like, so that the linewidth is compressed. The laser has the advantages that no internal grating is lost, the performance of the laser is excellent, the theoretical linewidth is very narrow, but the requirement on the external working environment is high, and various humiture, vibration and the like can influence the performance of the laser; the requirements on the coupling light paths of the optical elements are high, the optical elements are required to be precisely aligned, and the requirements on the packaging process are high.
Based on the defect that the preparation method in the prior art has the defect, through the preparation method of the laser provided by the embodiment of the application, the grating waveguide structure, the passive waveguide structure and the DFB structure can share one substrate, in the use process, the laser is excited by applying forward voltage to generate laser, part of the laser enters the passive waveguide structure from the grating waveguide structure, the two ends of the FP cavity of the passive waveguide structure are high in reflectivity, the FP cavity can not only promote the cavity length, but also can stabilize the wavelength of the laser for negative feedback of the DFB structure, and the linewidth is further compressed. The light has little loss in the passive waveguide structure. Through the arrangement of the grating waveguide structure, on one hand, the light of the laser can be efficiently coupled into the passive waveguide structure, meanwhile, high reflectivity can be provided for one end face of the passive waveguide structure, which cannot be coated by the FP cavity, so that the reflectivity of the FP cavity can be higher than 70%, the effect of compressing the line width can be well achieved, based on the laser provided by the embodiment of the application, the advantages of an external cavity optical feedback method and an internal cavity optical feedback method can be combined, the high-power DFB laser, the FP feedback cavity and the grating waveguide structure are monolithically integrated to form the high-performance narrow-line-width laser, the laser has the advantages of the external cavity optical feedback method and the internal cavity optical feedback method, the monolithic integration does not need a plurality of optical elements for coupling, the feedback cavity and the laser can be independently designed, and the cavity length of the resonant cavity is not limited by the internal loss of the DFB laser. In addition, the high-efficiency coupling of the laser and the FP feedback cavity is truly realized by arranging the grating waveguide structure, and the high-reflectivity optical fiber can provide high reflectivity for one end surface of the FP cavity, which cannot be coated with a film, so that the feedback effect of the FP cavity is improved.
As shown in fig. 3 to 7, in one possible embodiment, the step of preparing the grating waveguide structure on the substrate includes: growing a first silicon oxide film and a polysilicon film on a substrate; etching the polysilicon film to form a polysilicon grating layer; depositing silicon nitride on the polysilicon grating layer to form a silicon nitride layer; depositing a second silicon dioxide film on the silicon nitride grating cover layer; the first silicon oxide film, the polysilicon grating layer, the silicon nitride layer, and the second silicon oxide film are etched to form a grating waveguide structure on the substrate.
In this technical scheme, there is further provided a step of preparing a grating waveguide structure, which mainly includes the steps of: growing silicon oxide and polysilicon films on an InP substrate, wherein the thickness of the films depends on the design of a laser, and the growing equipment can flexibly use various chemical vapor depositions;
first lithography: and the part to be etched leaks out by using a standard photoetching process, the part not to be etched is protected by using photoresist as a mask, then the polysilicon film is etched to a certain depth by using dry etching to form a grating, the photoresist is removed, and the grating period depends on the wavelength of the laser.
Silicon nitride deposition: after etching, silicon nitride regrowth is carried out, the refractive index of silicon is 3.48, the refractive index of silicon nitride is 2.0, the alternating growth of high and low refractive index films is realized through the process, and the reflectivity and the projection ratio of the multilayer film can be determined by the film thickness and the cycle number.
Silicon oxide deposition: after the grating is manufactured, silicon oxide deposition is performed again, and the effect after deposition is shown in fig. 6. The refractive index of the silicon oxide is 1.44, and the polysilicon grating and the silicon nitride grating cover layer not only realize the function of adjusting the transmittance, but also provide the function of a slab waveguide, thereby realizing the efficient coupling of the laser and the FP cavity.
And (3) secondary photoetching: on a wafer on which silicon oxide is deposited, exposing a part to be etched by utilizing a photoetching technology, and etching the part by utilizing RIE (reactive ion etching) to the etching depth: directly etched to the substrate.
The polysilicon is carved into the grating by photoetching, and then a silicon nitride grating cover layer is covered, so that the reflectivity can be controlled by the grating period, and the problem that the FP cavity close to the DFB end cannot be coated is solved; in addition, through the selection of film materials, namely silicon and silicon nitride are selected as a grating layer and a waveguide layer, and silicon dioxide is selected as a cladding, the integration of the waveguide coupling device and the multilayer film reflectivity control device is realized;
as shown in fig. 8, in one possible embodiment, the step of preparing a passive waveguide structure on the substrate and on one side of the grating waveguide structure includes: shielding the grating waveguide structure and a portion of the substrate; a lower cladding layer, a waveguide layer and an upper cladding layer are sequentially grown on the substrate and positioned on one side of the grating waveguide structure; wherein, the preparation materials of the lower cladding layer and the upper cladding layer comprise InP materials, and the preparation materials of the waveguide layer comprise InGaAsP and/or AlGaInAs materials; wherein the bandgap of the material used to make the waveguide layer is greater than the bandgap of the material used to make the multiple quantum well layer of the DFB structure.
In this technical scheme, there is further provided a specific step of preparing a passive waveguide structure, the main steps including:
three times of photoetching: and (3) performing one-time photoetching, and blocking the area occupied by the DFB structure and the grating waveguide structure area by utilizing the dielectric film to leak out the area needing the epitaxial passive waveguide.
Passive waveguide epitaxy: and epitaxially growing a lower cladding layer, a waveguide layer and an upper cladding layer in sequence in the passive waveguide region. The cladding material is InP material the same as the substrate, the waveguide layer material is InGaAsP or AlGaInAs material, and the cladding material is undoped in the epitaxial growth process. The band gap of the passive waveguide material is larger than that of the multiple quantum well of the DFB laser, for example, the lasing wavelength of the laser is 1.55um, the band gap of the passive waveguide material can be 1.35-1.5um, the lasing wavelength of the laser is 1.31um, and the band gap of the passive waveguide material can be 1.1-1.25um. The epitaxial 3 layers of films, the 3 layers of materials are unstrained, and the materials are high in growth quality and small in optical loss due to no doping and no component gradual change.
As shown in fig. 9, in one possible embodiment, the step of fabricating a DFB structure on the substrate and on the other side of the grating waveguide structure includes: shielding the grating waveguide structure and the passive waveguide structure; growing an InP doped buffer layer on the substrate and on the other side of the grating waveguide structure; growing an N-type light limiting layer on the buffer layer to form a first limiting layer; growing a multi-quantum well layer on the first confinement layer; growing an intrinsic second confinement layer on the multiple quantum well layer; growing a P-type electron blocking layer on the second limiting layer; growing a first InP spacing layer on the P-type electron blocking layer, forming an etching stop layer on the InP spacing layer, and then growing a second InP spacing layer on the etching stop layer; preparing a grating on the second InP spacer layer; growing a grating covering layer with gradually increased doping concentration on the grating; and sequentially preparing a protective layer and an ohmic contact layer on the grating covering layer.
In this technical scheme, there is further provided a step of preparing a passive waveguide structure, mainly comprising the steps of:
four photolithography: the DFB structure is leaked out through one-time photoetching, and the passive waveguide structure and the grating waveguide structure are covered by the dielectric film;
growing an N-type doped InP Buffer layer on an N-type InP substrate;
growing an N-type light limiting layer on the buffer layer as a first limiting layer;
then growing a multi-quantum well layer on the first limiting layer;
growing an intrinsic upper limiting layer on the multiple quantum well layer to serve as a second limiting layer;
growing a P-type electron blocking layer on the second limiting layer to serve as an electron blocking layer;
growing a P-type InP spacer layer on the electron blocking layer, then growing a P-type InGaAsP layer as an etching stop layer of a subsequent ridge waveguide process, and then growing a P-type InP spacer layer to facilitate grating manufacture;
utilizing electron beam exposure technology or holographic grating technology to make grating, and then growing a layer of P-type InP grating cover layer to form the grating cover layer;
then growing a layer of P-type InP cladding with gradually increased doping concentration as a cladding;
and (3) growing an ohmic contact layer: the ohmic contact layer comprises 3 layers, two layers of InGaAsP with different band gaps are firstly grown, one layer of InGaAs contact layer is secondly grown, the 3 layers are all heavily doped in a P type, and the two layers of InGaAsP have the effect that the band gaps gradually transition from InP to InGaAs. The process grows a film structure of the DFB laser; the corrosion stopping layer can prevent the subsequent corrosion ridge waveguide structure from being corroded; heavily doped InGaAs can reduce the laser resistance;
in one possible embodiment, the method of making further comprises: a first electrode is formed on the DFB structure and a second electrode is formed on a side of the substrate facing away from the grating waveguide structure, the passive waveguide structure and the DFB structure.
It can be appreciated that the preparation method of the laser can further comprise a chip process flow: the standard process flow for RWG-DFB from the grown epitaxial wafer to the chip is shown in fig. 10. And the P-surface electrode process is completed by the grown epitaxial wafer through 5 times of photoetching. Specifically, the first lithography is to transfer the shape of the ridge to the wafer, and then the structure of the ridge waveguide is made by dry etching and wet etching; the second photoetching is carried out to make cleavage channels of the chip, and the chip is cleaved into single chip reserved positions subsequently; the third photoetching is a windowing process, and a dielectric film window is formed on the ridge to form a structure for limiting a current channel; the fourth photoetching can make electrodes meeting the requirements to be on the surface of the wafer through electron beam evaporation or magnetron sputtering; fifth photoetching is carried out to thicken the electrode through an electroless plating or electroplating process.
After the P-surface electrode process is finished, the thickness of the wafer subjected to thinning process is 90-130nm, and a layer of Ti/Pt/Au electrode is sputtered on the back of the wafer after the thinning process is finished to serve as an N-surface electrode. After the wafer process is finished, the wafer is cleaved into bar strips, then the bar strips are clamped for coating, the passive waveguide end face is coated with a high-reflectivity film, and the DFB end face is coated with a high-transmissivity film. And the bar after coating is cleaved into single chips for testing, packaging, ageing and the like.
In the present invention, the terms "first," "second," "third," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance; the term "plurality" means two or more, unless expressly defined otherwise. The terms "mounted," "connected," "secured," and the like are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; "coupled" may be directly coupled or indirectly coupled through intermediaries. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art according to the specific circumstances.
In the description of the present invention, it should be understood that the directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "front", "rear", etc. are based on the directions or positional relationships shown in the drawings, are merely for convenience of describing the present invention and simplifying the description, and do not indicate or imply that the devices or units referred to must have a specific direction, be constructed and operated in a specific direction, and thus should not be construed as limiting the present invention.
In the description of the present specification, the terms "one embodiment," "some embodiments," "particular embodiments," and the like, mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. A laser, comprising:
a substrate;
a grating waveguide structure disposed on the substrate;
the passive waveguide structure is arranged on the substrate and is positioned at one side of the grating waveguide structure;
the DFB laser structure is arranged on the substrate and positioned on the other side of the grating waveguide structure;
the grating waveguide structure includes:
the first silicon oxide cladding layer, the polysilicon grating layer, the silicon nitride grating cover layer and the second silicon oxide cladding layer are sequentially arranged upwards to the substrate;
the refractive index of the polysilicon grating layer is larger than that of the first silicon oxide cladding layer and the second silicon oxide cladding layer, the refractive index of the silicon nitride grating covering layer is larger than that of the first silicon oxide cladding layer and the second silicon oxide cladding layer, and the refractive index of the silicon nitride grating covering layer is smaller than that of the polysilicon grating layer;
the polysilicon grating layer is provided with a plurality of first convex parts, the silicon nitride grating covering layer is provided with a plurality of second convex parts, and the second convex parts are positioned between two adjacent first convex parts;
the first convex part and the second convex part have the same height and different widths, and the widths of the first convex part and the second convex part meet the following formula:
d＝(2m+1)λ/4n
wherein d is the width of the first convex part and the second convex part, n is the refractive index of each layer of material, m is a positive integer lambda is the lasing wavelength of the laser.
2. The laser of claim 1, wherein the passive waveguide structure comprises:
the lower cladding layer, the waveguide layer and the upper cladding layer are sequentially arranged upwards from the substrate;
wherein the lower cladding layer, the waveguide layer and the upper cladding layer are undoped.
3. The laser of claim 1, wherein the DFB structure comprises:
the buffer layer, the lower limiting layer, the multiple quantum well layer, the upper limiting layer, the electron blocking layer, the first spacing layer, the corrosion stopping layer, the second spacing layer, the grating covering layer, the cladding layer and the ohmic contact layer are sequentially arranged upwards to the substrate;
wherein the thickness of the lower confinement layer is 200nm to 500nm, the thickness of the upper confinement layer is 80nm to 120nm, and the thickness of the electron blocking layer is 20nm to 50nm.
4. The laser of claim 1, further comprising:
a first electrode layer overlying the DFB structure;
a second electrode layer covering a side of the substrate facing away from the grating waveguide structure, the passive waveguide structure, and the DFB structure;
wherein the substrate is an InP substrate.
5. A method for producing a laser, characterized by being used for producing the laser according to any one of claims 1 to 4, the method comprising:
preparing a grating waveguide structure on a substrate;
preparing a passive waveguide structure on the substrate and positioned at one side of the grating waveguide structure;
and preparing a DFB structure on the substrate and positioned on the other side of the grating waveguide structure.
6. The method of manufacturing according to claim 5, wherein the step of manufacturing the grating waveguide structure on the substrate comprises:
growing a first silicon oxide film and a polysilicon film on the substrate;
etching the polysilicon film to form a polysilicon grating layer;
depositing silicon nitride on the polysilicon grating layer to form a silicon nitride grating cover layer;
depositing a second silicon dioxide film on the silicon nitride grating cover layer;
and etching the first silicon oxide film, the polysilicon grating layer, the silicon nitride grating cover layer and the second silicon oxide film to form the grating waveguide structure on the substrate.
7. The method of manufacturing according to claim 6, wherein the step of manufacturing a passive waveguide structure on the substrate and on one side of the grating waveguide structure comprises:
shielding the grating waveguide structure and a portion of the substrate;
a lower cladding layer, a waveguide layer and an upper cladding layer are sequentially grown on the substrate and positioned on one side of the grating waveguide structure;
wherein, the preparation materials of the lower cladding layer and the upper cladding layer comprise InP materials, and the preparation materials of the waveguide layer comprise InGaAsP and/or AlGaInAs materials;
wherein the bandgap of the material used to make the waveguide layer is greater than the bandgap of the material used to make the multiple quantum well layer of the DFB structure.
8. The method of fabricating a DFB structure on the substrate and on the other side of the grating waveguide structure according to claim 5, comprising:
shielding the grating waveguide structure and the passive waveguide structure;
growing an N-type doped InP buffer layer on the substrate and on the other side of the grating waveguide structure;
growing an N-type light limiting layer on the buffer layer to form a lower limiting layer;
growing a multi-quantum well layer on the lower confinement layer;
growing an intrinsic upper confinement layer on the multiple quantum well layer;
growing a P-type electron blocking layer on the upper limiting layer;
growing a first InP spacer layer on the P-type electron blocking layer, forming an etching stop layer on the InP spacer layer, and then growing a second InP spacer layer on the etching stop layer;
preparing a grating on the second InP spacer layer;
growing a grating covering layer with gradually increased doping concentration on the grating;
sequentially growing a cladding layer and an ohmic contact layer on the grating covering layer;
the preparation method further comprises the following steps:
a first electrode is formed on the DFB structure and a second electrode is formed on a side of the substrate facing away from the grating waveguide structure, the passive waveguide structure, and the DFB structure.
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| CN108649426A (en) * | 2018-04-24 | 2018-10-12 | 青岛海信宽带多媒体技术有限公司 | A kind of laser |
| CN110401105A (en) * | 2019-08-12 | 2019-11-01 | 武汉敏芯半导体股份有限公司 | Single chip integrated narrow linewidth laser and production method |
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| CN1838492A (en) * | 2006-04-24 | 2006-09-27 | 何建军 | Q-modulation semiconductor laser |
| CN102496851A (en) * | 2011-11-24 | 2012-06-13 | 上海宏力半导体制造有限公司 | Laser and manufacturing method thereof, resonance cavity and manufacturing method thereof |
| CN108649426A (en) * | 2018-04-24 | 2018-10-12 | 青岛海信宽带多媒体技术有限公司 | A kind of laser |
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